用PIV研究内狭缝喷嘴流动及其对液体片状破裂的影响

In this work the influence of the internal flow field on the liquid film was investigated. A strategy for reliable PIV measurements inside of nozzle channels with a height of only a few hundred micrometers and at flow velocities of several m/s has been developed. These PIV measurements provided 2 dimensional snapshots of the velocity field inside the nozzle as well as velocity- and fluctuation-profiles across the channel. The development of the channel flow could be observed along the channel length at laminar and partly turbulent flow conditions. Disturbances were introduced to the flow field by inserting a wire into the channel flow. PIV measurements showed the resulting change of the nozzle flow (in the wake of the wire and without wire, respectively). The resulting effects on the free liquid film were observed using back-lit photographs and perpendicular lightsections through the film surface. In the case of the undisturbed nozzle, velocity fluctuations occurred mainly in the boundary layer and the fluctuations in main streamwise direction were dominant. The free liquid film of this nozzle was smooth at the exit and only at higher Re numbers the growth of surface waves could be observed further downstream. The nozzle with inserted wire showed a high level of velocity fluctuation in the center of the flow. Here, the fluctuations normal to the walls were of the same magnitude as the fluctuations in streamwise direction. The liquid film of this nozzle was roughened directly below the nozzle exit, even at low Re numbers. The high level fluctuations normal to the wall are assumed to play the dominant role in this process. These measurements demonstrate the influence of the internal flow field on the liquid sheet. The results of the present work agree well with recent experiments of Heukelbach and Tropea [1] and supplement the existing experimental data which for example can be used as input or validation of numerical simulations.